This invention relates to shifting stem metering valves that usually do not seat. Metering valves, especially when used in process control applications, must continually modulate or throttle flow with frequent position changes required of the actuating and metering elements of the valve. These valves have a metering passage that connects an inlet and an outlet passage. The metering passage is arranged to receive a tapered metering element. Extending away from the tapered metering element is a valve stem that is actuated axially to enlarge or decrease the area of the metering passage. Of course, an actuator passage must be provided in the valve body extending away from the metering passage. In conventional valve designs, the valve stem extends through the valve body and is actuated by elements connected to it outside of the valve body. The stem is surrounded by a ring or rings of packing that maintain the pressure within the valve.
This invention relates to magnetically actuated packless valves for high pressure applications. A related patent that pertains to a magnetically actuated valve, but not especially for high pressure applications, is U.S. Pat. No. 2,289,574. A more or less typical packed rising stem valve is illustrated in U.S. Pat. No. 3,269,698. Aspects of this invention relate to my own U.S. Pat. No. 4,106,825.
Shifting stem metering valves used in control applications (that is, where the stem is continuously being moved in response to process conditions, etc.) are typically designed such that the stem slides back and forth in the packing within a very short distance and/or the stem rotates no more than about one revolution during maximum axial travel. This limited movement of the stem protects the packing but is a limitation on the configuration of the metering orifice and the tapered metering element which cooperates therewith.
The known advantage of magnetically actuated valves is the elimination of the stuffing box or packing which has always been a drawback. Elimination of the stuffing box or packing is particularly desirable in the case of control valves in which the actuating element is frequently moved. However, in the past, magnetically actuated valves have been confined to relatively low pressures if at all used. The principal reason has been that sufficiently strong permanent magnets did not exist that would actuate the magnetic valve through the thick walls required to contain high pressures. Newly available permanent magnets permit the use of thicker walls in the valve housing providing the possibility of magnetically actuated valves for use at high pressures.
It is an object of this invention to provide a magnetically actuated valve for high pressures which will reliably adjust flow at minimal torques (applied by the drive magnets to the driven magnets) even at pressures in excess of 2000 psi. It is a further object to provide a magnetically metering valve that is pressure tight at pressures exceeding 10,000 psi and which can be opened against a sealing pressure of over 10,000 psi. It is a further object to provide a magnetically actuated valve with a value stem turnable through a plurality of revolutions about its axis in moving through its full throttling range.